Boys base layers from Deux par Deux add warmth under a snowsuit without limiting movement on the ski hill or at recess. Choose a two-piece thermal underwear set with a half-zip top, a one-piece thermal suit, or a merino wool set, all made to be worn as the first layer.

The two-piece set comes in thick brushed jersey with a smiley face print and an elastic-waist pant, in sizes 2 to 14. One-piece thermal suits in a blue gradient dinosaur print, a blue and beige gradient or a smiley face print have an asymmetrical zipper and run from 6 months to size 14, and the black merino wool set comes in sizes 2/3 to 12/14. For babies, see baby boys base layers.

Put them under boys snowsuits, keep hands warm with mittens and gloves, and see boys winter clothing for the rest of his cold-weather outfit.